The main problem that is nowadays intrinsic to the telecommunication networks is a problem of switching capacity overload due to the growing amount of calls transmitted over the networks. Bulky streams of calls and call attempts flowing to and from subscribers of the networks result in degradation of quality of the basic service which is offered by telephone networks, namely—the voice service. Up to a particular moment, regular telephone networks, such as PSTN, equipped with conventional public switches (which can also be called Local Switches, Local Exchanges or Central Offices) coped with more and more increasing use of telephone lines to handle data traffic (for example, on Internet), though very quickly the required bandwidth and the growing volume of the data traffic posed a serious problem and led to the necessity that the traffic load be divided. The main idea of sharing the traffic load was to transmit the high rate data, in the digital form, via separate networks suitable for transmitting data, such as packet networks like ATM, IP, Frame relay and the like.
One of practical solutions for overcoming the above problem is described in a publication WO97/39563, which proposes a method and apparatus for providing bypass networks in a telephone system. The bypass networks permit all forms of traffic on a telephone system, including various forms of data traffic, to be handled without resulting in significant degradation in service to customers while facilitating the controlled growth of the telephone system to handle rapidly increasing classes and levels of traffic. This is accomplished by providing one or more bypass networks in the system, with at least one class of traffic being diverted through such bypass network so as to utilize shared resources of the system. In the WO 97/39563, the idea of bypassing is described and illustrated with respect to the data traffic constituting the source of congestion in the system, while for the voice traffic of a particular local switch subscribers the basic route via the local loop and the local switch is preserved.
There is, however, another problem in the modem combined networks which has not yet been recognized enough and thus has not yet met its solution. Today, the traditional voice traffic, normally handled by its appropriate local loops and local switches, can be “protected” from invasion of new developing classes of traffic by diverting the data traffic to bypass networks. However, while these new developing classes of traffic have led to developing of new networks for transmission, the voice traffic still remains in the frame of the same capacities of local loops and local exchanges, which were calculated and built for some previously existed conditions. Furthermore, the need of temporary increasing/decreasing of the load may cause service degradation in the switched telephone networks.
Historically, a local switch capacity was usually selected with certain traffic load assumptions based on voice traffic characteristics so as to normally avoid overloading of the network. For example, depending on location, there might be four to eight times as many subscribers as there is switch capacity at a central office. Such systems have worked reasonably well with the number of lines and central office capacity being incrementally increased as the number of subscribers increases and only in rare circumstances does such a network become so overloaded that it is not possible to serve new call attempts properly (i.e., during peak traffic periods or anomalous conditions such as on holidays or where there is a catastrophe in the area).
It should also be noted that expenses for increasing capacity of a central office (local switch) are usually very high and operators would prefer not to upgrade them but to support the existing networks infrastructure.